A device such as a computer, a cell phone or a personal digital assistant (PDA) usually comes with a keyboard, and a press key structure of a computer keyboard as shown in FIG. 1 is a press key 10 with an elastic scissors-like mechanism. Compared with a traditional press key, the scissors-like press key 10 is advantageous in its long traveling path, evenly distributed acting force, and low noise, so that such press key is used extensively in thin-type keyboards, particularly the keyboards of notebook computers in recent years. The press key 10, disposed on a substrate 20 is composed of: a U-shaped first support arm 11, being pivotally coupled to a pivotal connecting shaft 13, and a second support arm 12 mounted on the first support arm 11. In addition, two position arm 111 are respectively arranged at the two sides of the first support arm 11 in a manner that each of which pieces through a position plate 21 mounted on the substrate 20 at positions corresponding to the two position arm 111. Since a vast majority of substrates 20 are made of metal, the position plate 21 can be formed by stamp forming, as those shown in FIGS. 2A and 2B. Each position plate 21 has a hole 211 for the position arm 111 to pass therethrough, so that the press key 10 can be pressed to move reciprocally along a direction F that is perpendicular to the extending of the substrate 20. When the press key 10 is not subjected to a pressing force, the first support arm 11 and the second support arm 12 can be forced to tilt upward from the substrate 20 by an elastic member (not shown in the figure) in a form of a scissor-like structure, as indicated by the dotted line in FIG. 2B. If the press key 10 is pressed, the first support arm 11 and the second support arm 12 are pressed flatly onto the substrate 20. To assure a smooth movement of the press key 10, the hole 211 and the position arm 111 are engaged loosely with a predetermined gap D. In addition, factors such as the tolerance of the size of the position plate 21, the distance between two position plates 21, and the size of the first support arm 11, and the existence of the aforementioned gap D may cause the press key 10 to shift and wobble, and thus affecting the overall stability of the press key when it is pressed, or even causing a malfunction of the press key when the pressing position is not aligned precisely.